John Herschel (1792-1871), distinguished astronomer, was a staunch supporter of the engines. He and Babbage met while undergraduates at Cambridge where they both studied mathematics. They remained lifelong friends. Herschel supported Babbage through personal encouragement, service on the Royal Society committees specially convened to advise on the utility of the engines, and through his advocacy for continued government investment in their construction. In 1827, shattered by the death of his wife, father and second son in the space of a year, Babbage sought solace with the Herschels in Slough in the rural outskirts of London. When Babbage left shortly after for an extended tour of the Continent, it was to Herschel that he entrusted the construction of the Engine. The press attacked Babbage while he was away. One article questioned the utility of the engines and impugned Babbage's financial probity. Herschel publicly came to Babbage's defense robustly justifying Babbage and his work.

Herschel made groundbreaking contributions to astronomy, photography, and philosophy. He became a model ambassador for science, respected, balanced, sound, and diplomatic. He attempted to restrain his friend's excesses especially Babbage's public diatribes against the Royal Society and his sarcastic attacks on prominent figures. When shown a pre-publication draft of Babbage's vehement attack on the scientific establishment Herschel wrote that he deserved 'a good slap in the face' and that he should burn the manuscript. Babbage took no heed, published (in 1830) and was damned. The contrast between the two friends, and their relative success, is telling. Herschel died five months before Babbage. In a letter to his widow Babbage described Herschel as 'one of the earliest and most valued friends of my life'.